#include <string>

class LibError{};

class CharError: LibError{};

class FileError: LibError{};

class LendError: LibError{};

class NoSuchMember: LibError{};

class NoSuchBook: LibError{};

class Impossible: LibError{};

class OutOfIDs: LibError{};

namespace Input{

std::string tolower(const std::string&);

int getNumber();

std::string getISBN();

}

namespace Crypt{

std::string encrypt(const std::string&);

std::string decrypt(const std::string&);

int NumberOf(char);

char CharOf(int);

}

void WaitForEnter();